You can use floating-point fields as mapped fields in logical files. A single- or double-precision floating-point field can be mapped to or from a zoned, packed, zero-precision binary, or another floating-point field. You cannot map between a floating-point field and a nonzero-precision binary field, a character field, a hexadecimal field, or a double-byte character set (DBCS) field.
Mapping between floating-point fields of different precision, single or double, or between floating-point fields and other numeric fields, can result in rounding or a loss of precision. Mapping a double-precision floating-point number to a single-precision floating-point number can result in rounding, depending on the particular number involved and its internal representation. Rounding is to the nearest (even) bit. The result always contains as much precision as possible. A loss of precision can also occur between two decimal numbers if the number of digits of precision is decreased.
You can inadvertently change the value of a field which your program did not explicitly change. For floating-point fields, this can occur if a physical file has a double-precision field that is mapped to a single-precision field in a logical file, and you issue an update for the record through the logical file. If the internal representation of the floating-point number causes it to be rounded when it is mapped to the logical file, then updating the logical record causes a permanent loss of precision in the physical file. If the rounded number is the key of the physical record, then the sequence of records in the physical file can also change.
A fixed-point numeric field can also be updated inadvertently if the precision is decreased in the logical file.